A Re-Evaluation of 235U, 238U And 239Pu Cross-Sections Based on Microscopic and Integral Data

A generalized least-squares method to improve microscopic cross-section evaluations by means of integral data, has been applied to re-evaluate the cross-sections of 235U, 238U and 239Pu, using critical-mass data of 24 simple metallic systems, composed of these isotopes. It has been found that, after some minor modifications of the original cross-section set, most of the experimental integral data could be reproduced. The cross-section modifications, as a rule, were of the order of a few per cent and well within the uncertainties in the cross-sections. The exception to the rule was the 239Pu fission cross-section in the energy range up to about 150 keV, which had to be decreased by 15 - 20%. This result independently confirms the recent measurements of White et al. (author)